1. Field of the Invention
The present invention relates to a display device, and more particularly, to a stereoscopic image display device and a method for manufacturing the same, in which switching between a two-dimensional image and a three-dimensional image is performed using an electro-wettable material depending on whether a voltage is applied.
2. Discussion of the Related Art
It is expected that services for high rate information based on a high speed information communication network will be developed from a simple type service such as ‘hearing and speaking’ service of a phone to a multimedia type service such as ‘seeing and hearing’ service based on a digital terminal, which processes text, audio, and video. Ultimately, it is expected that the simple type service will be developed to a three-dimensional stereoscopic information communication service that allows a user to stereoscopically see, feel and enjoy beyond the realm of time.
Generally, a stereoscopic image that expresses a three-dimension is obtained by the principle of stereo vision through two eyes. Since binocular parallax, i.e., the distance between two eyes is about 65 mm, the left eye and the right eye see different images from each other due to such a difference in their positions. The difference between images due to the difference in positions of two eyes will be referred to as binocular disparity. The three-dimensional stereoscopic display device allows the left eye to see an image only on the left eye and the right eye to see an image only on the right eye by using the binocular disparity.
In other words, left/right eyes see different two-dimensional images, and if the two images are transferred to the brain through the retina, the brain mixes the images with each other to reproduce depth and reality of the original three-dimensional image. This ability will generally be referred to as stereography, and if this ability is applied to a display device, the device will be referred to as a stereoscopic display device.
Meanwhile, the stereoscopic display device can be divided depending on elements that realize 3-dimension (3D). For example, a driving mode of the stereoscopic display device, which drives the stereoscopic display device to have a light path difference such as a lens by using a liquid crystal layer, will be referred to as a liquid crystal field lens mode.
Generally, a liquid crystal display device includes two electrodes facing each other, and a liquid crystal layer formed between the two electrodes, wherein liquid crystal molecules of the liquid crystal layer are driven by the electric field generated by applying a voltage to the two electrodes. The liquid crystal molecules have polarization properties and optical anisotropy. In this case, the polarization properties means that molecular arrangement is switched depending on the electric field as electric charges in the liquid crystal molecule are grouped at both sides if the liquid crystal molecule is arranged in the electric field. The optical anisotropy means that a path or polarizing state of emitting light is switched depending on an incident direction or polarizing state of incident light due to a thin and long structure of the liquid crystal molecule and the molecular arrangement.
In this case, the liquid crystal layer shows the difference in transmittance due to the voltage applied to the two electrodes and displays images by varying the difference per pixel.
Recently, a liquid crystal lens electrically driven has been developed, in which the liquid crystal layer serves as a lens by using the properties of the liquid crystal molecule.
In other words, the lens controls the path of the incident light per position by using the difference in refractive index between a material constituting the lens and the air. If the liquid crystal layer is driven by forming the electric field generated by applying a different voltage to each position of the electrodes, the incident light upon the liquid crystal layer brings different phases per position. As a result, the liquid crystal layer can control the path of the incident light like the actual lens.
Hereinafter, a general liquid crystal field lens will be described with reference to the accompanying drawings.
FIG. 1 is a sectional view illustrating an effect of the difference in light path of a general liquid crystal field lens.
The general liquid crystal field lens includes first and second substrates facing each other, and a liquid crystal layer formed between the first and second substrates.
In this case, a first electrode is formed on the first substrate at a first distance from the first substrate, and a second electrode is formed on the second substrate.
Liquid crystals are arranged depending on the electric field formed between the first electrode and the second electrode when a voltage is applied, whereby an effect similar to that of the lens can be obtained by the difference in light path caused by arrangement of the liquid crystals per region as shown in FIG. 1. In this case, as the strongest electric field is applied to the center of the first electrode, the liquid crystal lies down, whereby the shortest light path is obtained. If the liquid crystal becomes far away from the center of the first electrode, it becomes erect, whereby the light path becomes longer, and an effect like a parabolic lens is obtained.
The aforementioned liquid crystal field lens is attached to the display device, and displays a stereoscopic image depending on the voltage is applied.
In this case, the display device and the liquid crystal field lens require a process of respectively forming independent panels and bonding the panels to each other. When the panels are bonded to each other, miss-alignment between a lens area of the liquid crystal field lens and a pixel of the display device may occur. This means that three-dimensional display cannot be performed normally.
Also, as the liquid crystal field lens and the display device are independently provided, they require at least two glass substrates, respectively. In order to obtain a stereoscopic image display device, at least four glass substrates are required. For this reason, problems occur in that it is difficult to obtain a slim device and the cost and process steps are increased.
As described above, the aforementioned stereoscopic image display device according to the related art has the following problems.
The stereoscopic image display device based on a liquid crystal field lens is obtained by filling a liquid crystal layer between upper and lower substrates of a display device at a certain thickness and attaching the liquid crystal filed lens, which serves as a lens depending on that a voltage is applied, thereto.
In this case, at least four glass substrates are required, whereby the cost and thickness are increased. Also, in case of the liquid crystal field lens, the liquid crystal layer requires a thickness more than the height of the desired lens, whereby a long time is required to form the liquid crystal layer having the thickness and the liquid crystal may not be filled fully. Also, misalignment may occur in the bonding process of the liquid crystal field lens and the display device. Accordingly, it is required that the aforementioned stereoscopic image display device should be formed at a different structure to have a slim size.
As the case may be, in addition to the liquid crystal field lens, a lenticular lens sheet may be attached to the display device. In this case, problems occur in that misalignment may occur between the lenticular lens sheet and the display device and image switching between a two-dimensional image and a three-dimensional image cannot be performed.